I. Field of the Invention
The present invention relates generally to an object detection method and apparatus and, more particularly, to such an apparatus and method for use with an automotive vehicle.
II. Description of Related Art
There are many previously known patents in which one or more sensors are mounted to an automotive vehicle. These sensors generate sequential sensor pulses and, likewise, detect the reflection or echo of the pulse from a near object. Typically, the sensors are ultrasonic sensors.
Such sensors are particularly useful in automotive applications for assisting in parking of the automotive vehicle. For example, in previously known systems, ultrasonic sensors generate ultrasonic pulses laterally outwardly from both sides of the car. Any stationary object, such as a parked car, reflects the ultrasonic pulse back to the sensor from the closest perpendicular surface of the object. Consequently, the elapsed time between the transmission of each electronic pulse and the receipt of its reflection or echo from the stationary object directly corresponds to the distance between the motor vehicle and the closest perpendicular surface on the stationary object. In automotive parking assist systems the system provides the appropriate signal or alarm to the occupant of the motor vehicle of the distance between the motor vehicle and the stationary object.
One disadvantage of these previously known systems, however, is that, while such systems perform satisfactorily when the reflective surface of the stationary object is both aligned with and normal to the direction or axis of the sensor pulse, such systems suffer from inherent errors where the reflective surface of the stationary object is a curved surface with respect to the direction of the sensor pulse.
For example, when the direction of the reflection from the stationary object is significantly offset from the direction of the sensor axis, the distance between the sensor and the object is less than the distance calculated solely as a function of the elapsed time between the sensor pulse and receipt of its echo. Consequently, in order to protect the vehicle from collision with the stationary object, it has been the previous practice for such systems to include extra distance between the distance calculated from the elapsed time between the sensor pulse and receipt of its echo and the stationary object as a safety factor. This, however, disadvantageously limits the use of such systems in a cramped or close environment.
A still further disadvantage of these previously known systems is that in some cases the strength of the reflection from the perpendicular surface on the stationary object which is offset from the sensor axis may not be strong enough to exceed the threshold of the sensor. This, in turn, results in inaccuracies of the distance calculation between the stationary object and the sensor.